1. Field of Invention
The invention relates to plasticized polymer moldings made from modified polyvinyl butyrals and to methods for their preparation and their use. The modified polyvinyl butyrals (PVBs) are useful in plasticized form, for example, as interlayer films having improved rheological and mechanical properties for the production of glass laminates.
2. Description of Related Art
As is known, plasticizer-containing polyvinyl butyrals have long been processed in large amounts as thermoplastics. In particular, they have been extruded to give films which are used as interlayers in multilayer silicate laminate glasses, preferably for motor vehicle windshields, architectural glasses for the construction industry and for bulletproof glass screens.
It is known that the penetration resistance of a finished glass laminate is affected by the mechanical properties of the laminating film. Therefore, very high film strengths are desired.
It is furthermore known that the rheological behavior of plasticized PVB compositions is of great importance in laminate production, in particular in prelaminate production. Thus, the actual laminate production in the autoclave is preceded by a further process step. In this so-called prelamination process, a prelaminate is deaerated under pressure in a heating zone from 60.degree. to 110.degree. C. The high quality of the prelaminate produced in this way is a prerequisite for the production of the final laminate in the autoclave. The flow behavior of the film in the above-mentioned temperature range plays a crucial role here. Thus, inadequate flowability of the film results in incomplete contact between the silicate glass sheets and the laminating film. This is caused by thickness variations in the film and by glass flexing defects, which can result in visible glass delamination and air bubbles.
Between adequate flowability of the film and the highest possible film strength, there is an optimization problem. Thus, for example, increased film strength can be achieved by reducing the plasticizer content. However, this likewise results in lower flowability of the films. Polyvinyl butyrals having an increased proportion of free hydroxyl groups have higher film strengths, but likewise exhibit reduced flowability levels. A further disadvantage of these polyvinyl butyrals having an increased hydroxyl group content is the incompatibility with certain plasticizers, for example dihexyl adipate, which can result in exudation of the plasticizer.
EP-A 0 368 830, 0 368 831 and 0 368 832 describe polyvinyl butyrals containing sulfonate groups in side chains, plasticized polyvinyl butyral films produced therefrom and films made from blends of standard polyvinyl butyrals containing no sulfonate groups and polyvinyl butyrals containing sulfonate groups. These are ionomeric polyvinyl butyrals which are prepared from standard polyvinyl alcohols containing no sulfonate groups by acetalation by means of aldehydes containing sulfonate groups. A disadvantage here is the risk of recleavage of the aldehydes containing sulfonate groups, which can result in undesired secondary reactions. In addition, the particularly preferred aromatic aldehydes containing sulfonate groups impart undesired UV sensitivity on the laminating film, which can result in discoloration or degradation reactions in the laminating film on corresponding exposure of a glass laminate. A further disadvantage is the relatively high price of aldehydes containing sulfonate groups. These disadvantages prevent the films from being used on a large industrial scale as laminating films in glass laminate screens.